Switched mode power supplies (SMPS) are known in the art to convert an available direct current (DC) level voltage to another DC level voltage. A SMPS provides a regulated DC output voltage to a load by selectively storing energy in an output inductor coupled to the load by switching the flow of current into the output inductor. A buck converter is one particular type of SMPS that includes two power switches that are typically provided by MOSFET transistors. An inductor plus capacitor (LC) filter is used to reduce the ripple in output voltage. A pulse width modulation (PWM) control circuit is used to control the gating of the power switches in an alternating manner to control the flow of current in the output inductor. The PWM control circuit uses feedback signals reflecting the output voltage and/or current level to adjust the duty cycle applied to the power switches in response to changing load conditions.
Generally, buck regulators have high efficiency and are often used to regulate power for audio power amplifiers (PA), such as Class H PA. A buck regulator generates a supply voltage having envelope that varies continuously with an audio input signal of the PA. For high audio input signal amplitudes, a buck regulator typically operates in Class D mode, also known as a pulse-width modulation (PWM) mode. For lower audio input signals, the buck regulator typically switches to a pulse-frequency modulation (PFM) mode. In audio applications, a buck regulator typically includes an external low-pass LC filter having resonance frequency (Fres) of about 62 KHz (e.g., L=3 uH C=2.2 uF) for filtering out high-frequency components of the pulsed DC signal generated by the buck regulator. However, if during mode switching of the buck regulator, input audio signals close to Fres are injected into the LC filter, the filter output may exhibit peaking, which is undesirable for typical audio applications. Therefore, there is a need for a mechanism to suppress output voltage peaking in the LC filter of the buck regulator.